Electroplating bath



Patented June 21, 1932 UNITED STATES PATENT OFFICE".

JOHN I. K. MCCULLOUGH, OF DETROIT, MICHIGAN, AND BENJAMIN W. GILCHRIST, OF

EAST ORANGE, NEW JERSEY, ASSIGNORS TO TERNSTEDT MANUFACTURING COM- PANY, 0F DETROIT, MICHIGAN, A CORPORATION OF MICHIGAN .ELECTROPLATING BA'IH No Drawing.

This discovery relates to a new electroplating bath and particularly to gold, silver, copper, brass, or bronze or zinc plating baths.

.In plating with these metals, particularly with copper for example, it has been the practice recently where large production of copper plating is used to use a double cyanide bath: that is, a bath made up of sodium eyanide and copper cyanide together with an excess of free sodium cyanide. This sodium cyanide combines with the water of solution and the carbon-dioxide of the air to rorm sodiumcarbonate and at the same time there .is liberated poisonous hydrocyanic acid gas.

" from to F., with the gold solution,

which is run between160 and 180 F. and the copper solution which is run at about or F. and sometimes as high as the destructiveness of the sodium cy anide and hence poor anode corrosion 1S quite pronounced. Furthermore, in all these plating solutions, the free sodium cyanide is dissipated by reason of. its reaction with the water of solution and the carbon-dioxide of 'the air to form a hydrocyanic acid gas. This excess sodium cyanide, we prepare a bath in which the sodium cyanide and the copper cyanide are exactly in the proportions at which they combine to form a double cyanide.

Application filed October 7, 1929. Serial No. 398,088.

With the other metal plating baths, this is substantially the practice but in all events, we take the double salts and eliminate the excess sodium cyanide. Other ingredients may or may not be present with these other baths. When we say the double salts, we mean that in each of these baths there is present the double salts of the metal and an alkali metal such as sodium cyanide or potassium cyanide. Vith the brass and bronze which are alloys, one takes the double salts of the two metals, to wit: sodium zinc cyanide and sodium copper cyanide; with bronze there is present, ordinarily, sodium copper cyanide and sodium zinc cyanide with considerably less zinc than is the case with the brass solution and the bath is run at a considerably higher temperature so as to plate out more of the copper.

In all these baths, we have found that in place of the excess sodium cyanide, we can use the Rochelle salts, to wit: sodium-potassium-tartrate. We find that in the copper solution it is desirable to add caustic soda. We find that with such a bath, especially when run, for instance, with copper, at 180 to 212 with a current of 4; to 6 volts very good anode corrosion, conductance and clear deposits of copper take place.-

As an example of a copper bath, we use a solution that contains one ounce of copper cyanide to a gallon of Water and a half ounce of sodium cyanide to a gallon of water and two ounces of caustic soda and three ounces of Rochelle salts. with a range of these ingredients which can be used with good results:

7.5- 15 g./1.1 2 ozs. of copper cyanide 3.2- 7.5 g./1. .5-1 oz. of sodium cyanide 15 30 g/l. 2 22 120 4 ozs. of caustic soda g./l. 3-saturation of Rochelle salts.

Water-1 gallon Temperature preferred 180212 F. 6-volt current If, however, the proportions are not exact in starting, not a great deal of difiiculty will be encountered as the heat will soon dissipate the excess sodium cyanide and in case of an excess copper cyanide, this would be taken up bythe Rochelle salts to form a double tartrate of the copper and the alkali metal. This We give-below a table will result in makin the solution blue, from 3. The bath claimed in claim 1 in which which no particular arm results. However, the voltage is approximately 6 volts. by adding more sodium cyanide, the double In testimony whereof we aflix our signatartrate of the copper and the alkali can be tures. changed back intothe double'cyanide and JOHN F. K. MCCULLOUGH.

the alkali tartrate. BENJAMIN W. GILCHRIST.

It is not necessary to schedule the propor tions in making up a bath of the other metal solutions as any chemist can figure out the 10 correct proportions of the ingredients that go to make up the double cyanide and substantially the same amount of Rochelle salts can be used-aswith the copper solution, although, experience will show that there can 15 be a variation of more or less of these salts. so

In the brass and bronze solution the caustic soda should be left out. It may or may not be used in the other solutions except that it is highly desirable with the copper solution. In place of the Rochelle salts, one can sub stitute alkali citrate, such, for instance, as

sodium or potassium citrate and also the alkali bitartrates suchas potassium bitartrate may be used. Caustic potash may be used I 25 instead of caustic soda. In the bronze, brass,

and silver solutions, ammonium tartrate can be substituted for Rochelle salts.

We find that electro-plating baths made up in this we result in deposits that are free so from strea s and of good color, that the solution has better throwing power, can be op-.

erated with a greater range of temperature, without decomposition (212 F.), can be operated with a greater range of current 35 density to say 10-100 amperes per square foot,

and reduces the bufiing cost. We estimate that the cost of this solution over a long run is onl about 17% of the excess cyanide solution or the reason that we obviate the necessityof addin sodium cyanide. 4 1 5 We might a (1 here that in these double solutions it is (possible, of course, to use potassium' cyani e but this is .rather costl and, of course, when the potassium cyani e 45 is used in the double cyanide, it is customary to use as the excess, potassium cyanide.

- What we claim is:

1. An electroplating bath comprising a double cyanide of the. metal, to be deposited and one of the two alkali metals, sodium and i potassium, and a double salt made up of one of a group of organic compound ingredients which consists of the tartrates and citrates 3 and one of the group of alkali metals, which consists of potassium, sodium and ammonium, the proportions for the copper bath being 1 to 2 ounces of copper cyanidefl/ to 1 ounce of alkali metal cyanide and 2 to 4' 00 ounces of caustic soda and 3 to 16 ounces of" the double salts of'the tartrate or citrate per gallon of water. i

2. The bath claimed in claim 1 inv which the temperature is approximately F. to

.66212F. lao 

